1. Field of the Invention
The present invention relates to an exposure apparatus and a method of manufacturing a device.
2. Description of the Related Art
Conventionally, in manufacturing a device such as a semiconductor device or liquid crystal device using photolithography, the pattern of an original is transferred by exposure via a projection optical system onto a photosensitive substrate coated with a photosensitive agent.
In recent years, along with further acceleration of an increase in the packing density of devices, micropatterning on a photosensitive substrate is making remarkable advances. Examples of exposure apparatuses that play a central role in micropatterning are a mirror projection aligner, stepper, and scanner. The mirror projection aligner is a non-scaled projection exposure apparatus which exposes a photosensitive substrate while scanning it and an original with respect to a non-scaled mirror optical system having an arcuated exposure region. The stepper is a reduction projection exposure apparatus which forms a pattern image of an original on a photosensitive substrate by a refractive optical system, thereby exposing the photosensitive substrate by the step & repeat scheme. The scanner is a reduction projection exposure apparatus which exposes a photosensitive substrate while scanning it in synchronism with scanning of an original.
These days, along with an increase in the resolution of a projection optical system mounted in a projection exposure apparatus, a strict demand has arisen for correction of the aberration of the projection optical system. It is therefore indispensable to measure and check the aberration of a projection optical system after mounting it into the main body of an exposure apparatus.
To meet these demands, Japanese Patent Laid-Open Nos. 2000-277411 and 2000-277412 each disclose an exposure apparatus which mounts an interferometer capable of measuring the aberration of a projection optical system in its main body.
The interferometer forms interference fringes using an aberration measurement pattern such as a pinhole having a diameter equal to or less than the diffraction limit of light or a slit having a width equal to or less than the diffraction limit of light, and measures the interference fringes using, for example, an image sensing element. Measurement methods that use a Fizeau interferometer and shearing interferometer are also available.
To measure the aberration of the projection optical system by an interferometer formed using fine aberration measurement patterns (for example, pinholes or slits), original-side and photosensitive-substrate-side aberration measurement patterns must be aligned with appropriate positions with high accuracy. The original-side aberration measurement pattern is formed on the original or in its vicinity, and the photosensitive-substrate-side aberration measurement pattern is formed on the photosensitive substrate or its vicinity.
There is a method of measuring, by an image sensing element or the like, the amount of light guided from the illumination optical system to it via the original-side aberration measurement pattern, projection optical system, and photosensitive-substrate-side aberration measurement pattern, and aligning the relative position between the original-side and photosensitive-substrate-side aberration measurement patterns. In this method, the correlation between an appropriate position and the light amount at this position is checked in advance, and a position at which a desirable light amount is measured by scanning one or both of the original-side and photosensitive-substrate-side aberration measurement patterns is determined as an appropriate position.
However, because each aberration measurement pattern is a micropattern having a size equal to or less than the diffraction limit of light, it is difficult to obtain the relative position between the original-side and photosensitive-substrate-side aberration measurement patterns. To measure an appropriate light amount by the light amount detector, it is necessary to frequently repeat scanning of one or both of the original-side and photosensitive-substrate-side aberration measurement patterns. Consequently, it takes a lot of time to align the aberration measurement patterns, which makes it impossible to timely measure the aberration of the projection optical system.